final methods and classes in Java

 

✅ Final Methods and Classes in Java

The final keyword in Java is a non-access modifier used to indicate that something cannot be modified. It can be applied to classes, methods, and variables.

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📌 1. Final Classes

A final class cannot be extended (inherited) by any other class. This is used when you want to prevent the class from being subclassed to protect its implementation.

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Syntax

final class FinalClass {

    void display() {

        System.out.println("This is a final class.");

    }

}

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Example of Final Class

final class Vehicle {  // Declaring a final class

    public void display() {

        System.out.println("Vehicle class display method.");

    }

}

 

// Attempt to inherit the final class (This will cause a compile-time error)

/*

class Car extends Vehicle {

    // Error: Cannot inherit from final 'Vehicle'

}

*/

 

public class Main {

    public static void main(String[] args) {

        Vehicle obj = new Vehicle();

        obj.display();

    }

}

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Output

Vehicle class display method.

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🔍 Explanation

• The class Vehicle is declared as final, which prevents any class from extending it.
• Trying to create a subclass like Car will result in a compile-time error.

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📌 2. Final Methods

A final method cannot be overridden by any subclass. This is useful when you want to ensure that the implementation of a method remains unchanged.

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Syntax

class Parent {

    final void display() {  // Declaring a final method

        System.out.println("This is a final method.");

    }

}

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Example of Final Method

class Parent {

    final void display() {  // Final method

        System.out.println("Final method in Parent class.");

    }

}

 

class Child extends Parent {

    // Attempting to override a final method (This will cause a compile-time error)

    /*

    void display() {  

        System.out.println("Trying to override final method.");

    }

    */

}

 

public class Main {

    public static void main(String[] args) {

        Parent obj = new Parent();

        obj.display();

    }

}

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Output

Final method in Parent class.

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🔍 Explanation

• The method display() in the Parent class is declared as final.
• Attempting to override display() in the Child class will result in a compile-time error.

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📌 3. Important Points to Remember

1. Final Classes:
• Prevent inheritance.
• Commonly used to create immutable classes (e.g., String class in Java).
2. Final Methods:
• Prevent overriding.
• Useful when a method's functionality must remain consistent across all subclasses.
3. Use Cases:
• Security: Prevent unauthorized overriding.
• Performance: The compiler may optimize final methods since it knows they won't be overridden.
• Immutability: Creating immutable classes by making classes final and providing only final fields.

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